1. Field of the Invention
The present invention relates to a chemical vapor deposition (CVD) method of supplying a reaction gas to a substrate and forming a thin film having a prescribed composition on the substrate surface by chemical reaction in a vapor phase or that caused on the substrate surface, and a CVD treatment system and a CVD apparatus therefor.
2. Description of the Background Art
FIG. 17 is a front sectional view showing a principal part of a conventional normal-pressure CVD apparatus. A reaction housing 1 is formed by a reaction housing body 2 and a reaction housing head portion 3, so that its internal space (reaction space 4) is isolated from the outside air. A substrate support 5 supports a semiconductor substrate 6 in the reaction space 4. This substrate support 5 comprises a heater 7 and a soaking plate 8. The substrate support 5 so supports the semiconductor substrate 6 as to horizontally maintain both major surfaces thereof while downwardly directing one major surface (treated major surface) 9 to be provided with a thin film by chemical reaction. The soaking plate 8 vacuum-sucks a rear major surface 10 of the semiconductor substrate 6, to closely fix the semiconductor substrate 6. A reaction gas introduction plate 11 is provided to face the treated major surface 9, and reaction gas introduction holes 12 are provided in this reaction gas introduction plate 11 in a region substantially opposite to the treated major surface 9. The reaction housing head portion 3 is provided with an exhaust passage 13 which is opened toward the reaction housing 4, and a central axis 14 of this exhaust passage 13 is inclined toward the surface of the substrate 6 to be circumferentially separated from the edge of the semiconductor substrate 6 in relation to the reaction space 4. The reaction housing 1 is provided with a carrier passage 15 for introducing the semiconductor substrate 6 from the exterior into the reaction space 4 and discharging the former from the latter, while a gate 16 is provided for closing the carrier passage 15, thereby isolating the reaction space 4 from the outside air. The gate 16, which can be freely opened and closed, is opened when the semiconductor substrate 6 is introduced or discharged into or from the reaction space 4. A reaction gas mixing chamber 17 is provided in connection to the reaction gas introduction plate 11 in an opposite side of the reaction space 4, receiving the semiconductor substrate 6, in relation to the reaction gas introduction plate 11. The reaction gas mixing chamber 17 is provided with a plurality of reaction gas supply holes 18a and 18b.
The operation of this apparatus is now described. The gate 16 is opened to insert the semiconductor substrate 6 in the reaction space 4 through the carrier passage 15. The soaking plate 8 closely fixes the semiconductor substrate 6. A first reaction gas 21a which is prepared from silane gas (SiH.sub.4) and a second reaction gas 21b which is prepared from oxygen gas (O.sub.2), for example, are supplied into the reaction gas mixing chamber 17 from the reaction gas supply holes 18a and 18b respectively. The reaction gas mixing chamber 17 mixes such a plurality of types of reaction gases 21a and 21b with each other The as-mixed reaction gas 21 is injected into the reaction space 4 through the reaction gas introduction holes 12. Heat generated by the heater 7 is uniformly transferred to the overall semiconductor substrate 6 through the soaking plate 8. Due to such heat, the reaction gas 21 causes thermochemical reaction such as oxidation, for example, so that the reaction product of silicon dioxide (SiO.sub.2) is deposited on the treated major surface 9 to form a thin film. An exhaust gas containing a reaction residue gas and the like is continuously discharged to the exterior of the reaction space 4 through the exhaust passage 13. When a thin film of a prescribed thickness is formed on the treated major surface 9, the gate 16 is opened and the semiconductor substrate 6 is separated from the soaking plate 8 to be discharged from the reaction space 4 to the exterior through the carrier passage 15. Since thin films are thus formed on a number of such semiconductor substrates 6, reaction byproducts 22 are gradually deposited on peripheries 23 of the reaction gas introduction holes 12 as the aforementioned operation is repeated.
The conventional CVD apparatus having the aforementioned structure requires a cleaning operation for removing the reaction byproducts 22 deposited on the peripheries 23 of the reaction gas introduction holes 12. Thus, the CVD apparatus must be periodically stopped for such cleaning operation, and hence the throughput of the apparatus is disadvantageously reduced. Further, the reaction byproducts 22 deposited on the peripheries 23 of the reaction gas introduction holes 21 are blown up when the semiconductor substrate 6 is introduced into or discharged from the reaction space 4, to stick onto the semiconductor substrate 6 as foreign matters. Thus, the yield of finished semiconductor devices, which are formed on the basis of such semiconductor substrates 6, is disadvantageously reduced.